The present invention relates to a variable swirl siamese type intake port structure for an internal combustion engine cylinder head, and more particularly relates to a siamesed such variable swirl siamese type intake port structure for an internal combustion engine cylinder head, which incorporates two intake valves and a switchover valve construction for selectively supplying intake air - fuel mixture to said valves in varying proportions, and which is improved as regards gas flow resistance and volumetric efficiency in various engine operational conditions.
The present patent application has been at least partly prepared utilizing materials which were disclosed in Japanese patent application Ser. No. 60-129035 (1985) and the present patent application hereby incorporates into itself by reference the disclosure of said Japanese Patent Application and of the claims and of the drawings thereof; a copy of said Japanese Patent Application is appended to this application.
In the prior art, there are various types of intake port structures for internal combustion engine cylinder heads, and in particular for so called siamese type cylinder heads. Such intake port structures typically are of the variable swirl siamese type, in which the siamesed intake port comprises a generally straight intake passage and a generally helical intake passage arranged in parallel with said generally straight intake passage, so that both said generally straight intake passage and also said generally helical intake passage receive supply of intake air - fuel mixture from the engine intake manifold, with a control valve selectively at least partially interrupting the flow of air - fuel mixture through said straight intake passage, so as selectively provide extra swirl for the intake air - fuel mixture being sucked into the combustion chamber of the engine, so as to improve combustibility, flame front propagation speed, and firing efficiency and thereby militate against engine knocking, thereby to allow the engine to be operated with a weaker intake air - fuel mixture than would otherwise be practicable. Such a construction typically includes a separating wall which divides between said generally straight intake passage and said generally helical intake passage. And a prior art to the present patent application, Japanese patent application Ser. No. 56-143215 which has been laid open as Japanese Patent Laying Open Publication Ser. No. 58-48715 and which was filed by an applicant the same as the applicant of the Japanese patent application of which the priority is being claimed in the present application and to whom either the present application is assigned or is owed a duty of assignment of the present application, discloses an improved siamesed type intake port structure for an internal combustion engine cylinder head which is provided with a bypass air passage through said separating wall, connecting a point on the generally straight intake passage downstream of said control valve provided therein to a vortex end wall of the generally helical intake passage.
With such an intake port structure for an internal combustion engine cylinder head, when the control valve is controlled to be in the closed state by a control system therefor, all of the air - fuel mixture sucked in by the combustion chamber of the engine is inhaled through the generally helical intake passage, and is accordingly imparted with strong swirling; this mode of operation is appropriate for when the engine is operating at low load, as during the idling engine operating condition. However, at this time the resistance presented to flow of air - fuel mixture by the generally helical intake passage alone is high. On the other hand, when the control valve is controlled to be in the open state by the control system therefor, most of the air - fuel mixture sucked in by the combustion chamber of the engine is inhaled through the generally straight intake passage with only a minor proportion thereof being inhaled through the generally helical intake passage, and accordingly the inhaled air - fuel mixture as a whole is imparted with relatively weak swirling, thus accordingly causing the volumetric efficiency of the engine to be high so as to develop good engine power; this mode of operation is appropriate for when the engine is operating at high load, such as full load. At this time the resistance presented to flow of air - fuel mixture by the combination of the generally straight intake passage and the generally helical intake passage is relatively low, and is improved by the provision of the above mentioned bypass air passage, according to the above identified prior proposal. However, the generally helical intake passage still has a relatively high resistance to flow of air - fuel mixture, and this is the greater the more said generally helical intake passage is constructed to provide strong swirl, so an obstacle is still presented to the desirable increase of engine output power.